AbstractPeroxisome proliferator-activated receptor alpha (PPARa) and delta (PPARd) belong to the nuclear receptor superfamily. PPARa is a target of lipid-lowering drugs and PPARd promotes fatty acid utilization and is a promising anti-diabetic drug target. However, evidence is growing that PPARd-agonism can stimulate fat accumulation in liver, which may aggravate the toxic situation in diabetics.
The aim of the study was to characterise the hepatic transcriptional and lipid response of humanized mouse models to PPARd-agonists.
In our studies of mice conditionally-expressing human PPARd (hPPARd), or the dominant-negative derivative of hPPARd (hPPARd?AF2) or wild-type animals, we demonstrated that GW501516, a potent PPARd activator, promoted up-regulation of the genes involved in lipid turnover, stimulated significant weight loss and promoted hepatic steatosis in these mouse models. There was time-dependent accumulation of hepatic triglycerides observed in wild-type and in conditionally-expressing hPPARd mice fed a diet containing PPARd synthetic ligand. This was not seen in animals conditionally-expressing hPPARd?AF2, neither in PPARa-KO or PPARd-KO animals. Concurrently, activation of PPARd in humanised animals caused significant depletion, as compared with controls, of adipose tissue deposits when fed normal or high fat diet. This effect was completely absent in PPARa-KO or PPARd-KO mice, fed diet containing GW501516. Genome-wide transcriptional profiling of GW501516 effects in the livers of these different mouse strains was performed. In PPARa-KO mice fed PPARd-agonist, some direct PPARd target genes were still up-regulated, demonstrating that they are not sufficient for the observed phenotype. In addition the blood HDL-raising effects of GW501516 were preserved in the PPARa-KO mice.
This suggests a novel finding that both PPARd and PPARa receptors are essential for GW501516-driven weight loss and hepatic steatosis, with PPARa working downstream of PPARd.
|Date of Award||2012|
|Sponsors||Medical Research Council|
|Supervisor||Colin Palmer (Supervisor)|
- Peroxisome Proliferator Activator Receptor (PPAR)